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<h1 align=center style='text-align:center'>预处理命令</h1>

<p class=MsoNormal><span lang=EN-US style='font-family:"Tahoma","sans-serif";
color:#555555;background:white'>&nbsp;</span><span style='font-family:宋体;
color:#555555;background:white'>在前面各章中，已多次使用过以</span><span lang=EN-US
style='font-family:"Tahoma","sans-serif";color:#555555;background:white'>“#”</span><span
style='font-family:宋体;color:#555555;background:white'>号开头的预处理命令。如包含命令</span><span
lang=EN-US style='font-family:"Tahoma","sans-serif";color:#555555;background:
white'>#include</span><span style='font-family:宋体;color:#555555;background:
white'>，宏定义命令</span><span lang=EN-US style='font-family:"Tahoma","sans-serif";
color:#555555;background:white'>#define</span><span style='font-family:宋体;
color:#555555;background:white'>等。在源程序中这些命令都放在函数之外，而且一般都放在源文件的前面，它们称为预处理部分。</span><span
lang=EN-US style='font-family:"Tahoma","sans-serif";color:#555555'><br>
<br>
</span><span style='font-family:宋体;color:#555555;background:white'>所谓预处理是指在进行编译的第一遍扫描</span><span
lang=EN-US style='font-family:"Tahoma","sans-serif";color:#555555;background:
white'>(</span><span style='font-family:宋体;color:#555555;background:white'>词法扫描和语法分析</span><span
lang=EN-US style='font-family:"Tahoma","sans-serif";color:#555555;background:
white'>)</span><span style='font-family:宋体;color:#555555;background:white'>之前所作的工作。预处理是Ｃ语言的一个重要功能，它由预处理程序负责完成。当对一个源文件进行编译时，系统将自动引用预处理程序对源程序中的预处理部分作处理，处理完毕自动进入对源程序的编译。</span><span
lang=EN-US style='font-family:"Tahoma","sans-serif";color:#555555'><br>
<br>
</span><span style='font-family:宋体;color:#555555;background:white'>Ｃ语言提供了多种预处理功能，如宏定义、文件包含、条件编译等。合理地使用预处理功能编写的程序便于阅读、修改、移植和调试，也有利于模块化程序设计。本章介绍常用的几种预处理功能。</span></p>

<p class=MsoNormal><span lang=EN-US>&nbsp;</span></p>

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